Rain Cycle
This experiment shows the cycle of rain. Fill a third of a small paper cup with water. Carefully put the cup into a zipping plastic bag and close the bag. Tape it to a window that receives direct sunlight. Observe how the water begins to evaporate and appear on the bag in small droplets. As the droplets connect and grow, they drip or run down the bag. This experiment demonstrates evaporation, condensation and rainfall.
Making Rain
When warm, rising moisture in the air meets cooler air higher in the atmosphere, condensation occurs. Make your own condensation by putting water in a tea kettle and, with adult supervision, boiling the water on the stove. After a while, steam begins rising from the kettle, representing evaporation. Place ice cubes on a pie tin and hold the pie tin over the kettle's steam (protect your hands with oven mitts). When the bottom of the cold pie tin meets the hot evaporated water, condensation forms on the bottom of the pie tin. When enough water accumulates and grows heavier, drops begin falling from the tin, simulating how rain forms inside clouds.
Mutual Attraction
Water molecules are attracted to other water molecules in the air. You can demonstrate this using two straws and a single glassful of water. Grab one straw with each hand and dip the straws into a glass of water evenly. Take the straws out and hold them together, so they're touching. Much like the small water molecules in a cloud, the water on both straws will attract and combine, mostly on one straw. If the combined water is heavy enough, it will fall from the straw, just like a raindrop from a cloud.
Making Clouds
This experiment illustrates how clouds form. Because hot water and matches are used, parental supervision is recommended. Tear the labeling off a clear 2-liter bottle, then fill one-third of the bottle with warm water. Let it sit for a few hours and droplets form on the upper portions of the bottle. Squeeze the bottle to remove the droplets. Remove the lid and and light a match, holding it close to the bottle's opening. Drop it in the bottle and quickly screw on the lid. Squeeze the bottle and release it a few times. You'll notice that when you release pressure, a cloud begins to form, but disappears as you squeeze. These squeezes and releases represent the rise and fall of air pressure, which forms a cloud with water and smoke.